U.S. Pat. No. 3,151,816, which issued to Hanse et al in 1964, discloses an impact crusher of the general type to which this invention relates. The patent points out that the hammer bars on the rotor of such a device "are severely abused by the conditions under which the apparatus is operated", and that they should therefore be readily replaceable. It also points out that the hammer bars should nevertheless be securely locked to the rotor structure in such a manner that the high centrifugal and impact forces to which they are subjected do not loosen them and require them to be retightened from time to time. In the rotor that the patent discloses, the radial slot in which each hammer bar is seated defines opposing front and rear surfaces relative to the direction of rotor rotation, and the rear one of these slot-defined surfaces has a rearward undercut in which a rearward projection on the hammer bar is received for hook-like securement of the hammer bar against radially outward displacement by centrifugal force. For releasable locking of the hammer bar there is a wedge in the slot into which a screw is threaded that reacts against the front surface of the slot. Cooperating oblique surfaces in the slot, on the wedge and on the hammer bar translate the rearward force that the screw exerts on the wedge into a rearward and radially outward force on the hammer bar whereby the rearward projection on it is maintained firmly seated in the undercut and engaged against the radially inwardly facing abutment that the undercut defines.
A major disadvantage of this arrangement is that the hammer bar must necessarily be so configured that it can be installed in the rotor structure in only one position and orientation. Its impacting surface must project radially beyond the rotor structure periphery by a predetermined distance, and when that surface becomes excessively worn the hammer bar must be discarded and replaced, with no possibility of its being reversed or otherwise reoriented to bring another of its surfaces into use as an impact surface.
In U.S. Pat. No. 3,170,643, issued to Hanse et al in 1965 and disclosing another impact crusher of the general type here under consideration, very little is said about the manner in which the hammer bars are secured to the rotor structure other than that "they are releasably mounted in place as by means of wedges 21 so that they may be removed and replaced when wear has occurred." The drawings are sketchy and somewhat ambiguous with respect to the wedges, which appear to be so arranged that centrifugal force could throw them out of the rotor structure.
U.S. Pat. No. 3,531,055, issued to Alt in 1970, discloses a rotor structure wherein each hammer bar has longitudinally extending grooves in a pair of its opposite faces, those in one face being in laterally staggered relation to those in the other. For each hammer bar, a retaining beam that is welded to the discs of the rotor structure and extends along the rear of the hammer bar has a longitudinal rib which engages in any selected one of the longitudinal grooves to fix the hammer bar radially in relation to the discs. With this arrangement the hammer bar is reversible so that either of its faces can serve as its front material-impacting surface, and it can also be adjusted to project radially at different incremental distances beyond the peripheries of the discs that carry it. However, the hammer bar does not seem to be engaged against the retaining beam under clamping or wedging force. Instead, it is merely confined against radially outward displacement by the rib on the retaining beam and against lengthwise displacement by bolts through the retaining beam which engage in transverse grooves in the hammer bar but are so oriented that they cannot exert a clamping force against it. Since each hammer bar can be removed from the rotor structure only by withdrawing it lengthwise therefrom, the hammer bars must either fit rather loosely in the disc slots so that they tend to rattle against the discs and retaining beams or their installation and removal from the rotor structure must be very difficult.
U.S. Pat. No. 3,784,117, issued to Koenig in 1974, discloses a rotor wherein the hammer bars are confined in radial disc slots that define front and rear surfaces which are radially outwardly convergent and thus obliquely oppose one another. A support bar mounted in a recess in the rear surface of each slot has a forwardly protruding longitudinal rib which engages in a longitudinal groove in the rear face of the hammer bar. For each slot in each disc a radially outwardly tapering wedge is confined between the front face of the hammer bar and the front slot surface and is urged radially outwardly by a pressure fluid operated element. The radially outward force that the hydraulic devices exert upon the wedges is translated by the latter into a rearward clamping force upon the hammer bar that maintains it firmly but releasably engaged with the support bar. The obvious disadvantage of this arrangement is that its hydraulic apparatus is complicated, expensive and not well suited to the rigors of an impact crusher environment.
U.S. Pat. No. 4,573,643, issued to Orphall et al in 1986, discloses a rotor having, for each hammer bar, a backup bar of circular cross-section which is secured to the rear of the disc slot that receives the hammer bar and which engages in a longitudinally extending arcuate groove in the hammer bar to fix the radial position thereof. In this case, too, a radially outward tapering wedge member in the disc slot confines the hammer bar against the backup bar. To restrict the wedge to radially in and out motion in the disc slot, a U-shaped clamping member straddles the peripheral portion of the disc and has legs that normally embrace the wedge. A bolt extends lengthwise parallel to the rotor axis through the wedge and the legs of the clamping member to constrain the wedge and clamping member to move as a unit in directions radial to the rotor axis. When the machine is in operation, centrifugal force maintains each wedge in secure clamping engagement with its hammer bar whereby the latter is in turn firmly confined against its backup bar; but some difficulty is involved in establishing the wedges initially in firm engagement with newly installed hammer bars so that they will be securely held in place during the first few slow revolutions of the rotor. For installation of a hammer bar the disc slots that are to receive it must be in or near the 3 o'clock position of rotor rotation, and to accommodate this limitation the rotor must be releasably locked against rotation out of that position.
U.S. Pat. No. 4,679,740, issued to Orphall in 1987, discloses a rotor wherein a circular-section backup bar cooperates with each hammer bar and with a wedge, essentially as in the above-discussed Orphall et al patent, but no U-shaped clamping member is needed because the wedge has ridges or lands which slidingly engage the axially opposite surfaces of the disc to confine the wedge against displacement parallel to the rotor axis. In addition, the radially inner portion of the wedge has side surfaces which are flush with the axially opposite side surfaces of the disc and which are overlain by a pair of plates that also overlie the side surfaces of the disc. These plates are connected with one another by means of a bolt that is lengthwise parallel to the rotor axis and extends through an enlargement or bay near the radially inner end of the disc slot. A sleeve around this bolt is selected to have an outside diameter such as to take up any clearance between the bottom of the bay and the wider radially inner end of the wedge, to establish the wedge in wedging engagement with the hammer bar immediately upon installation. The disadvantage of this arrangement is that small tolerances cannot very well be maintained in a rotor structure of the type here under consideration, so that the outside diameter of the sleeve tends to vary from wedge to wedge and therefore a sleeve of the required outside diameter must be found or made for each wedge. This arrangement also seems to require that the rotor be releasably locked against rotation for installation of each hammer bar.
From the foregoing brief review it will be apparent that securement of the hammer bars of an impact crusher rotor presents a complex set of requirements that have not heretofore ben fully satisfied. Thus, it has not been obvious to those working in the art how to provide simple, sturdy and inexpensive means for firmly but readily detachably securing the hammer bars to the rotor structure in an arrangement such that the hammer bars are both reversible and radially adjustable, are well supported against high impact and centrifugal forces by rotor structure that is both light and inexpensive, and can be quickly and easily installed, adjusted and removed.